My mechanic said my freeze plugs where shot .Can you tell me where are they and what are they .My truck is over heating in a very short period.

Freeze plugs are round, metal/aluminum plugs located in various spots on the engine block. Their purpose is to prevent the engine block from cracking in freezing weather IF you don't have anti-freeze in your car/truck. The plugs will pop out as the water freezes (and expands) releasing the water from the engine block. Kind of a safety-valve device.
I am questioning your "mechanics" dstatement that they are 'shot'. They are either good (not leaking) or bad (leaking). If they are "shot" then you should be loosing antifreeze all over the place. Ask your "mechanic" for a reasonable explanation for his diagnosis.
I would suspect something else other than the freeze plugs causing your overheating problem (i.e. stuck thermostat, clogged radiator, cooling fans not working, blown head gasket)...
I would try ANOTHER mechanic, maybe one recommended by a friend. Lots of so-called mechanics out there that couldn't fix a pedal car....

Freeze plugs r as described in 1st. post. Other wise known as frost plugs. Screw u & Yur dictionary. They serve two purposes. 1 wen engine was cast, but the main purpose is to pop out & relieve pressure from freezing ice!! The guy in the 1st. post was rite. & the 2nd. post peep shudn't b giving advice. He or she shud stick to reading & complaining about my spelling. Lol. I'm a mechanic not a **** lick like u. Lmao.

Freeze plugs are NOT designed as stated above!!!! They are simply the places where the mold of the engine was cast:
http://en.wikipedia.org/wiki/Core_plug
These 'Freeze plugs' are simply blocked unsused passegeways. To correct this the best possible way, I suggest you use Brass instead of aluminum or cast iron so it does not get eaten away by the coolant.
When engines are made, especially aluminum, they are made out of a styrafoam mold with sand around it. when the aluminum cools, the sand falls away, leaving the molded engine in place. The empty passesgeways enterances where the 'freeze-plugs' correctly called core-plugs, are needed to keep these passageways open during molding.